JP2010276748A - Fixing device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device including a fixing rotor having a heating means, an endless pressure belt disposed in pressure contact with the fixing rotor, a pressing member firmly pressing the pressure belt from the inside of the pressure belt and forming a nip portion between the fixing rotor and the pressing member itself, and a sheet member disposed between the pressing member and the pressure belt and used for reducing friction resistance between the pressing member and the pressure belt, the device being configured to suppress friction on both ends of the sheet member by reducing pressure on both the widthwise ends of the pressing member without damaging the fixing rotor. <P>SOLUTION: The corners of both ends of the pressing member 7 in a direction perpendicular to the direction of passage of paper P are given round shapes R. The round shapes R of the pressing member 7 are located outside the area of the passage of the paper P and at least a part of the round shapes R is located inside the axial ends of the fixing roller 6. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus including the fixing device, and more specifically, allows a member to be transferred to pass through a nip portion formed by pressing a fixing rotating body having a heating unit and a pressure rotating body. The present invention relates to a fixing device that heats and presses an unfixed toner image to melt and fix it on a transfer target member, and an image forming apparatus including the same.

  In an image forming apparatus having a facsimile, a printer, a copying machine, and a combination of these functions, an unfixed toner image formed on a member to be transferred passes through a nip portion between a fixing rotator and a pressure rotator. When this is done, it is heated and pressurized and melted and fixed on the transfer member (fixing process). The transferred member on which the toner image is fixed is guided by the guide member and discharged out of the image forming apparatus.

  In such a fixing device of the image forming apparatus, the fixing speed is increased, the generation of uneven fixing and paper wrinkles is prevented, the image quality is improved, the fixing device is downsized, and the fixing device at room temperature can be fixed. It is desired to shorten the warm-up time before starting up.

  Therefore, in order to meet this demand, a fixing system in which the pressure pad is pressed against the surface of the fixing roller having a heating means via an endless pressure belt to increase the nip width between the fixing roller and the pressure belt is practical. It has become.

  In this fixing method, since the nip width can be increased, the fixing process can be speeded up and the fixing device can be reduced in size, and the amount of heat taken away from the fixing roller to the pressure belt and pressure pad side can be reduced to reduce the nip portion. Therefore, the toner can be improved in fixability and the warm-up time can be shortened by reducing the amount of temperature drop in the toner and increasing the efficiency of using heat for melting the toner.

  In addition, in order to reduce the frictional resistance between the fixed pressure pad surface and the inner peripheral surface of the pressure belt, a sheet member having a small friction coefficient and wear resistance is used. The thing provided between the surfaces is also proposed (for example, refer patent document 1).

  However, when pressure is applied between the fixing roller and the pressure pad by applying a force to both ends in the axial direction, the pressing force is usually larger at both ends in the axial direction than at the central portion in the axial direction, so that the pressure belt slides. Both end portions of the sheet member are easily worn. Then, the shaving powder of the sheet member generated by the wear accumulates between the sheet member and the pressure belt, causing a change in torque of the pressure belt and abnormal noise. Therefore, the corners at both ends in the width direction of the pressure pad are chamfered to reduce the pressure at both ends in the width direction of the pressure pad, thereby suppressing the wear of the pressure belt.

JP 2005-331576 A

  In order to greatly reduce the pressure at both ends in the width direction of the pressure pad by chamfering, the inclined surface of the chamfering process needs to be steeply inclined. However, when the inclined surface of the chamfering process is steeply inclined, the pressing force changes abruptly at the portion where the inclined surface starts to be formed, so that the portion of the fixing roller that comes into pressure contact with the portion becomes severely damaged.

  The present invention has been made in view of such a conventional problem, and an object of the present invention is to reduce the pressure at both ends in the width direction of the pressing member without damaging the fixing rotator, and Both ends are to suppress wear.

  A fixing device according to the present invention that achieves the above object includes a fixing rotator having a heating means and a pressure rotator that presses against the fixing rotator to form a nip portion, and has an unfixed toner on one surface. A fixing device that heats and pressurizes a toner image by passing a nip portion through a transfer member on which an image is formed, and melts and fixes the transfer image onto the transfer member. The pressing rotator is attached to the fixing rotator. An endless pressure belt that comes into pressure contact, a pressure member that presses the pressure belt from the inside of the pressure belt and forms a nip portion with the fixing rotating body, and the pressure member and the pressure belt And a sheet member that reduces the frictional resistance between the pressing member and the pressure belt, and a direction perpendicular to the passing direction of the member to be transferred (hereinafter, “ The corners of both ends of the “width direction” may be round And it has a said rounded on the outside than the passage area of the transfer member, and, at least part of said rounded, characterized in that located inside the axial end portion of the fixing rotator.

  Here, from the viewpoint of elongating the nip portion and facilitating peeling of the transferred member from the fixing rotating body, the pressing member is composed of a soft pad portion and a hard pad portion elongated in the width direction of the transferred member, The soft pad portion and the hard pad portion are provided in this order with respect to the passing direction of the transferred member, and at least the corners of the hard pad portion that are perpendicular to the passing direction of the transferred member are rounded. preferable.

  The radius of curvature of the roundness is preferably 2 mm or more.

  According to the present invention, there is provided an image forming apparatus comprising the fixing device according to any one of the above.

  In the fixing device and the image forming apparatus of the present invention, the corners at both ends in the width direction of the pressing member are rounded, and at least a part of the rounding is located inside the axial end of the fixing rotating body. As a result, the pressure at both ends in the width direction of the pressing member can be reduced without damaging the fixing rotator. This makes it possible to effectively suppress wear at both ends of the sheet member. In addition, since the roundness of the corners at both ends in the width direction of the pressing member is located outside the passing region of the transferred member, it does not interfere with the fixing process of the transferred member that passes through the nip portion. Absent.

  The pressing member includes a soft pad portion and a hard pad portion that are elongated in a direction perpendicular to the passing direction of the member to be transferred, and the soft pad portion and the hard pad portion are formed with respect to the passing direction of the member to be transferred. Providing in this order and rounding at least the corners of the hard pad portion in the direction perpendicular to the passing direction of the member to be transferred can lengthen the nip portion. The size can be reduced, and the transfer member can be easily peeled off from the fixing rotating body.

  When the radius of curvature of the roundness is 2 mm or more, it is possible to further prevent damage to the fixing rotator and reduce pressure at both ends in the width direction of the pressing member.

1 is a schematic diagram illustrating an example of a fixing device and an image forming apparatus according to the present invention. 1 is a schematic diagram illustrating an example of a fixing device according to the present invention. It is an assembly perspective view of a pressing member and a sheet member. It is explanatory drawing which shows the formation position of the roundness of a press member. It is a perspective view which shows the other example of the press member used by this invention. It is a figure which shows distribution of the pressing force in a nip part. It is a figure which shows the difference in the abrasion of a sheet | seat member, and the damage of a fixing roller by the shape of the width direction both ends of a press member.

  Hereinafter, a fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus and a fixing device of the present invention. The image forming apparatus D in FIG. 1 is a so-called tandem color printer. Of course, in addition to a printer, the present invention can also be applied to a copying machine having a scanner, a facsimile, or a multi-function machine having these functions combined. Further, the image forming method is not limited to the tandem method, and other methods, for example, four developing devices are arranged around the rotation shaft, and these are sequentially opposed to the electrostatic latent image carrier to be full color. A so-called four-cycle method of creating an image or a monochrome method of creating a monochrome image with one developing device may be used.

  The image forming apparatus D includes an endless intermediate transfer belt 33 having conductivity. The intermediate transfer belt 33 is hung on a pair of rollers 31 and 32 disposed on both the left and right sides in the drawing. The roller 32 is connected to a motor (not shown), and the roller 32 rotates counterclockwise by driving the motor, whereby the intermediate transfer belt 33 and the roller 31 in contact therewith are driven to rotate. A secondary transfer roller 34 is in pressure contact with the outside of the belt portion supported by the roller 32. The toner image formed on the intermediate transfer belt 33 at the nip portion (secondary transfer region) between the secondary transfer roller 34 and the intermediate transfer belt 33 is transferred onto the conveyed paper P.

  A cleaning member 35 for cleaning the surface of the intermediate transfer belt 33 is provided outside the belt portion supported by the roller 31. The cleaning member 35 is in pressure contact with the roller 31 via the intermediate transfer belt 33, and untransferred toner is collected at the contact portion.

  Below the intermediate transfer belt 33 suspended between the rollers 31 and 32, yellow (Y), magenta (M), cyan (C), black ( K) four image forming units 2Y, 2M, 2C, and 2K (hereinafter may be collectively referred to as “image forming unit 2”). In these image forming units 2, corresponding color toner images are created using the respective color developers.

  The image forming unit 2 includes a cylindrical photoconductor 20 as an electrostatic latent image carrier. Around the photoconductor 20, a charger 21, a developing device 23, a primary transfer roller 24, and a photoconductor cleaning member 25 are arranged in this order along the rotation direction (clockwise direction). The primary transfer roller 24 is in pressure contact with the photoconductor 20 with the intermediate transfer belt 33 interposed therebetween to form a nip portion (primary transfer region). An exposure device 22 is disposed below the image forming unit 2.

  In the embodiment shown in this figure, a roller charging type is used as the charger 21, but the type of the charger 21 is not particularly limited, and a corona discharge charging charger, a blade-shaped charging member, Of course, a brush-like charging member or the like may be used. In this embodiment, a plate-like blade is used as the photosensitive member cleaning member 25, and one end thereof is brought into contact with the outer peripheral surface of the photosensitive member 20 to collect and remove toner remaining on the surface of the photosensitive member 20. The photosensitive member cleaning member 25 is not limited to a plate blade, and for example, a fixed brush, a rotating brush, a roller, and a combination of these members can also be used. Note that the photoconductor cleaning member 25 is not necessarily provided, and a cleanerless system in which the untransferred toner on the photoconductor 20 is collected by the developing device 23 may be employed.

  Above the intermediate transfer belt 33, hoppers 4Y, 4M, 4C, and 4K (hereinafter sometimes collectively referred to as “hopper 4”) containing toner to be supplied to the developing devices 23 of the respective colors are arranged. A paper feed cassette 50 is detachably disposed as a paper feed device below the exposure device 22. The sheets (transferred members) P stacked and accommodated in the sheet feeding cassette 50 are sent out one by one to the conveyance path in order from the uppermost sheet by the rotation of the sheet feeding roller 51 disposed in the vicinity of the sheet feeding cassette 50. The paper P sent out from the paper feed cassette 50 is conveyed to the registration roller pair 52 and is sent out to the secondary transfer area at a predetermined timing.

  The image forming apparatus D can be switched between a monochrome mode in which a monochrome image is formed using one color toner (for example, black) and a color mode in which a color image is formed using four color toners.

  An image forming operation example in the color mode will be briefly described. First, in each image forming unit 2, the outer peripheral surface of the photoreceptor 20 that is rotationally driven at a predetermined peripheral speed is charged by the charger 21. Next, light corresponding to image information is projected from the exposure device 22 on the surface of the charged photoconductor 20 to form an electrostatic latent image. Subsequently, the electrostatic latent image is made visible by toner as a developer supplied from the developing device 23. When the toner image of each color formed on the surface of the photoreceptor 20 in this way reaches the primary transfer region by the rotation of the photoreceptor 20, the toner image is transferred from the photoreceptor 20 to the intermediate transfer belt in the order of yellow, magenta, cyan, and black. 33 is transferred (primary transfer) and superimposed.

  Untransferred toner remaining on the photoconductor 20 without being transferred to the intermediate transfer belt 33 is scraped off by the photoconductor cleaning member 25 and removed from the outer peripheral surface of the photoconductor 20.

  The superimposed four color toner images are conveyed to the secondary transfer region by the intermediate transfer belt 33. On the other hand, the paper P is conveyed from the registration roller pair 52 to the secondary transfer area in accordance with the timing. Then, the four color toner images are transferred (secondary transfer) from the intermediate transfer belt 33 to the paper P in the secondary transfer region. The paper P on which the four color toner images are transferred is conveyed to the fixing device 1. In the fixing device 1, the paper P passes through the nip portion between the fixing roller 6 and the pressure rotator 7. During this time, the paper P is heated and pressurized, and the toner image on the paper P is melted and fixed on the paper P. A specific configuration of the fixing device 1 will be described later. The paper P on which the toner image is fixed is discharged to a paper discharge tray 54 by a discharge roller pair 53.

  On the other hand, the intermediate transfer belt 33 that has passed through the secondary transfer region is cleaned by the cleaning blade 35. Thereafter, the rotational drive of each photoconductor 20 and the intermediate transfer belt 33 is stopped.

  FIG. 2 is a schematic configuration diagram of the fixing device 1 mounted on the image forming apparatus D of FIG. The fixing device 1 includes a fixing roller 6 as a fixing rotating body that is rotationally driven, and a pressure rotating body 7 that is in pressure contact with the fixing roller 6. The fixing roller 6 incorporates a rod-shaped heater (heating means) 62 in the axial direction. A temperature sensor S is installed on the outer periphery of the fixing roller 6, and the heater 62 is controlled to be turned on and off by the temperature detected by the temperature sensor S, so that the surface of the fixing roller 6 is maintained at a predetermined temperature.

  The fixing roller 6 is formed by laminating a heat-resistant elastic body layer and a release layer (not shown) around a metal cylindrical cored bar 61 formed in a cylindrical shape having a predetermined length. The metal core 61 of the fixing roller 6 is preferably a metal having high thermal conductivity such as iron, aluminum, or SUS. The thickness of the cored bar 61 is preferably in the range of 0.1 to 5 mm, and more preferably in the range of 0.2 to 1.5 mm from the viewpoint of weight reduction and shortening of the warm-up time. In the fixing device 1, the pressing force of the pressing member 72 is smaller than usual, so that the outer shape and thickness of the cored bar 61 can be reduced in diameter and thickness.

  The material of the heat-resistant elastic layer of the fixing roller 6 is not particularly limited as long as it is a highly heat-resistant elastic body. However, it is preferable to use an elastic body such as rubber or elastomer having a rubber hardness of about 25 to 40 degrees. . Specifically, it is preferable to use silicone rubber, fluorine rubber, or the like. Although there is no limitation in the thickness of an elastic body layer, the range of 0.05-2 mm is preferable.

  Any resin may be used for the release layer of the fixing roller 6 as long as it is a heat-resistant resin. For example, a silicone resin, a fluorine resin, or the like can be used. From the viewpoint, a fluororesin is suitable. As the fluororesin, PFA, PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene hexafluoropropylene copolymer), or the like can be used. As a thickness of a mold release layer, the range of 5-100 micrometers is preferable, More preferably, it is the range of 10-30 micrometers. Further, the contact angle of the release layer with water is preferably 90 degrees or more, and more preferably 110 degrees or more. Further, the surface roughness Ra of the release layer is preferably in the range of 0.01 to 50 μm.

  Next, the pressure rotator 7 includes an endless pressure belt 71 that presses against the fixing roller 6, a pressure member 72 that presses the pressure belt 71 from the inside, a support member 74 that supports the pressure member 72, And a sheet member 73 disposed between the pressure belt 71 and the pressing member 72.

  Although the structure of the pressure belt 71 is not particularly limited, a structure having a base layer and a release layer formed on the surface or both surfaces of the base layer on the fixing roller side is preferable. As a base layer, metal materials, such as polymers, such as a polyimide, polyamide, a polyimide amide, and SUS, nickel, copper, are preferable, for example, The thickness has the preferable range of 30-200 micrometers, More preferably, it is the range of 50-150 micrometers. is there. The release layer formed on the surface of the base layer is preferably a fluororesin such as PFA, PTFE, FEP, etc., and its thickness is preferably in the range of 5 to 100 μm, more preferably in the range of 10 to 30 μm. . An elastic layer may be provided between the base layer and the release layer. As the elastic layer, a material having heat resistance and elasticity such as silicone rubber and fluororubber is desirable. Although there is no limitation in the thickness of an elastic layer, Usually, the range of 0.05-2 mm is preferable.

  Further, the inner peripheral surface of the pressure belt 71 reduces the surface roughness Ra in order to reduce the frictional resistance with the sheet member 73, while the outer peripheral surface of the pressure belt 71 has a driving force from the fixing roller 6. It is preferable to increase the surface roughness Ra so as to be easily received. The surface roughness Ra of the inner peripheral surface of the pressure belt 71 is preferably 0.4 μm or less, and the surface roughness Ra of the outer peripheral surface of the pressure belt 71 is preferably in the range of 1.2 to 2.0 μm.

  Next, the pressing member 72 is inside the pressure belt 71 and presses the pressure belt 71 against the fixing roller 6 with a predetermined pressure distribution via the sheet member 73. As a result, a nip portion N is formed by the fixing roller 6 and the pressure belt 71. Here, the nip portion N is a region where the fixing roller 6 and the pressure belt 71 are in rolling contact with each other while being elastically deformed, has a predetermined length in the passing direction of the paper P, and An area that is substantially rectangular in plan view over the axial direction of the fixing roller 6 is assumed. The pressing force applied to the nip portion N is usually preferably about 100 to 300N.

  The pressing member 72 has a soft pad portion 722 and a hard pad portion 723, and the soft pad portion 722 is disposed upstream of the nip portion N in the sheet passing direction. The soft pad portion 722 forms a long nip portion N with the fixing roller 6 and applies sufficient heat and pressure to the paper P. On the other hand, the hard pad portion 723 is disposed on the downstream side of the nip portion N in the sheet passing direction, strongly presses against the fixing roller 6, and includes a heat-resistant elastic body layer and a release layer provided on the outer periphery of the core metal of the fixing roller 6. The paper P is peeled off from the surface of the fixing roller 6 by being elastically deformed.

  FIG. 3 shows an assembly perspective view of the pressing member 72. The pressing member 72 includes a substantially quadrangular columnar main body 721 and a soft pad portion 722. A hard pad portion 723 extends outward substantially perpendicularly from one side surface of the main body portion 721, and an elongated groove 724 is formed upstream of the hard pad portion 723 in the sheet passing direction. A part of the quadrangular columnar soft pad portion 722 is fitted into the groove 724. Thereby, the soft pad portion 722 and the hard pad portion 723 are adjacent to each other in the sheet passing direction to form one pressing member 72. And the sheet | seat member 73 is attached so that the free end side of the soft pad part 722 and the hard pad part 723 may be covered.

  What is important here is that roundness R is provided at the corners in contact with the sheet member 73 at both ends in the width direction of the hard pad portion 723, as shown in the partial enlarged view of FIG. By providing the roundness R at the corner of the hard pad portion 723, the pressing force by the both ends of the hard pad portion 723 can be reduced without damaging the fixing roller 6, and the both ends of the sheet member 73 can be reduced. Wear is suppressed.

  In order to obtain the above-described effect by providing the roundness R at the corners at both ends in the width direction of the hard pad portion 723, as shown in FIG. 4, the rounding R is formed outside the sheet passage area. In addition, at least a part of the roundness R needs to be inside the both ends of the fixing roller 6 in the axial direction. If the roundness R provided at both ends in the width direction of the hard pad portion 723 is located in the paper passage region, sufficient pressing force is not applied to the paper P, and the toner image may be insufficiently glossy or offset. Further, when the roundness R provided at both ends in the width direction of the hard pad portion 723 is located outside the both ends in the axial direction of the fixing roller 6, both ends of the hard pad portion 723 do not face the fixing roller 6, and the effect of the present invention. Is not played.

  The radius of curvature of the roundness R at both ends in the width direction of the hard pad portion 723 is not particularly limited, and may be appropriately determined in consideration of the material of the hard pad portion 723 and the sheet member 73, the pressing force by the hard pad portion 723, and the like. Usually, 2 mm or more is preferable. The preferred upper limit value of the radius of curvature of the roundness R at both ends in the width direction of the hard pad portion 723 is 20 mm.

  In the embodiment shown in FIG. 3, the main body portion 721 and the hard pad portion 723 of the pressing member 72 are integrally formed. However, the hard pad portion 723 may be separately produced and then attached to the main body portion 721. Further, as shown in FIG. 5, as the pressing member 72 used in the present invention, a pressing member 72 that does not have a soft pad portion but has only a hard pad portion 723 may be used. Also in this case, it goes without saying that roundness R is provided at both ends in the width direction of the hard pad portion 723.

  The soft pad portion 722 used in the present invention can be composed of, for example, an elastic material such as silicone rubber or fluorine rubber, a leaf spring, or the like. Although there is no limitation in particular in the thickness of the soft pad part 722, the range of 0.1-10 mm is preferable. Further, the hard pad portion 723 can be made of a heat-resistant resin such as PPS (polyphenylene sulfide), polyimide, polyester, polyamide, or a metal material such as iron, aluminum, SUS, or the like.

  As the sheet member 73 used in the present invention, a sheet member having a small friction coefficient and excellent wear resistance and heat resistance is desirable. This is because the sheet member 73 is interposed between the pressure belt 71 and the pressing member 72 to reduce the sliding resistance between the pressure belt 71 and the pressing member 72. As such a sheet member 73, for example, a porous resin fiber cloth made of a fluororesin is used as a base layer and a PET resin sheet is wrapped on the surface on the fixing roller side, a sintered PTFE resin sheet, Teflon (registered trademark) Or the like can be used. Further, minute unevenness may be formed on the surface of the sheet member 73 on the pressure belt side so that the lubricant applied to the inner peripheral surface of the pressure belt can enter the sliding portion with the pressure belt 71. .

  The pressing member 72 assembled with the sheet member 73 is attached to a support member 74 as shown in FIG. The support member 74 is made of a metal such as aluminum and has a deformed cylindrical shape in which one corner of a substantially rectangular cross section is projected in a small arc shape.

  The support member 74 is provided with a lubricant application member 75 over the longitudinal direction on the outer surface of the side portion facing the mounting portion of the pressing member 72. The lubricant application member 75 is formed of a belt-like heat-resistant felt, and is impregnated with a lubricant such as amino-modified silicone oil having a viscosity of 300 cs, for example. The lubricant application member 75 is disposed so as to be in sliding contact with the inner peripheral surface of the pressure belt 71, and the inner peripheral surface of the pressure belt 71 is always in an appropriate amount by the osmotic pressure from the heat-resistant felt. To be supplied. In addition, it is desirable that the lubricant application member 75 is configured so that only the edge portion of the heat-resistant felt is in contact with the inner peripheral surface of the pressure belt 71 so that the lubricant is not excessively supplied from the heat-resistant felt. . Thereby, the lubricant is supplied to the sliding portion between the pressure belt 71 and the sheet member 73, and the sliding resistance between the pressure belt 71 and the pressing member 72 via the sheet member 73 is further reduced, and the pressure belt The smooth operation of 71 is achieved.

  In the fixing device shown in FIG. 2 having such a configuration, when the fixing roller 6 is rotated counterclockwise by a drive motor (not shown), the pressure belt 71 in pressure contact with the fixing roller 6 is driven to rotate. The conveyed paper P passes through the nip portion N so that the surface on which the unfixed toner image t is placed is on the fixing roller side. While passing through the nip portion N, the toner image t is heated and pressurized, and the toner image t is melted and fixed on the paper P. Then, the paper P is separated from the fixing roller 6 by the separation claw 63 and is discharged to the paper discharge tray 54 (shown in FIG. 1).

  Since the pressure belt 71 and the sheet member 73 are pressed by the pressing member 72 at the nip portion N, the pressure belt 71 and the sheet member 73 are rubbed to wear the sheet member 73. In the conventional fixing device, the wear of the sheet member 73 is particularly remarkable at both ends in the width direction of the pressing member 72. However, in the fixing device of the present invention, the corner portions at both ends of the hard pad portion 723 as the pressing member 72 are used. Since the rounding R is provided, the pressing force is reduced, and the wear of the sheet member 73 due to the friction with the pressure belt 71 is remarkably suppressed.

  In addition, as described above, if the lubricant is applied from the lubricant applying member 75 to the inner peripheral surface of the pressure belt 71, the sliding resistance between the pressure belt 71 and the pressing member 72 is reduced. Further, the wear of the sheet member 73 is further suppressed.

  The fixing rotator used in the fixing device according to the present invention is not limited to the fixing roller 6 including the heater 62 of the above-described embodiment. For example, a heat generation source as a heating unit is in pressure contact or close. Of course, it is also possible to use a fixing belt.

(Measurement of pressing force)
The pressing force at the axial position of the nip portion of the fixing device shown in FIG. 2 was measured. In addition, the curvature radius of the round shape of the width direction both ends of a hard pad part was 2 mm. As a comparison, the pressing force was also measured for the case where the corner portion was not provided with a round shape at both ends in the width direction of the hard pad portion. The results are shown in FIG.

  In FIG. 6, the vertical axis is the pressing force at the nip portion, the horizontal axis is the position in the width direction at the nip portion, and the shape of both ends in the width direction of the hard pad portion is rounded, and the corner portion is left as it is. It is a figure which shows the pressing force distribution in the case. As is clear from this figure, the pressing force at both ends in the axial direction of the nip portion is more than the case where the corner portions at the both ends in the width direction of the hard pad portion are rounded so that the portions remain as corner portions. It can be seen that the value also decreases.

(Comparison between rounded shape and chamfered shape)
Next, a comparison was made between the case where the shape of both end portions in the width direction of the hard pad portion was a rounded shape and the case of a chamfered shape. Specifically, as shown in FIG. 7, the angle of the inclined surface of the chamfering process is moderate (experiment a), and the angle of the inclined surface of the chamfering process is steep with a radius of curvature of about 2 mm (experiment b). The wear amount of the sheet member and the damage to the fixing roller were evaluated by visual observation when the radius of curvature of the round shape was 2 mm (experiment c). The results are shown in FIG.

  As apparent from FIG. 7, when the angle of the inclined surface of the chamfering process was made gentle (Experiment a), the fixing roller was slightly damaged, but the amount of wear of the sheet member was large. In addition, when the angle of the inclined surface of the chamfering process is steep (Experiment b), although the amount of wear of the sheet member is small, the pressing force changes abruptly at the portion where the inclined surface of the chamfering process starts to be formed. The roller was damaged. On the other hand, when the radius of curvature of the round shape is 2 mm (experiment c), the wear amount of the sheet member is small, and the change in the pressing force at both ends in the width direction of the hard pad portion is continuous. I couldn't see it.

(Influence of radius of curvature)
The curvature radius of the round shape at both ends in the width direction of the hard pad portion was set to 0.5 mm and 2 mm, and the torque change of the fixing roller and the presence or absence of abnormal noise of the fixing device were examined. In addition, for comparison, when the corner portion is not provided with a round shape, the torque change of the fixing roller and the occurrence of abnormal noise of the fixing device were examined in the same manner. Table 1 shows the survey results.

  When the curvature radius of the round shape at both ends in the width direction of the hard pad portion was 0.5 mm, a slight change in torque of the fixing roller and abnormal noise of the fixing device occurred. When the radius of curvature was 2 mm, no change in torque of the fixing roller and no abnormal noise of the fixing device occurred. On the other hand, when both end portions in the width direction of the hard pad portion are corner portions, a change in torque of the fixing roller and abnormal noise of the fixing device occurred remarkably.

  In the fixing device and the image forming apparatus of the present invention, the corners at both ends in the width direction of the pressing member are rounded, and at least a part of the rounding is located inside the axial end of the fixing rotating body. As a result, the pressure at both ends in the width direction of the pressing member can be reduced without damaging the fixing rotator. This is useful because it can effectively suppress wear at both ends of the sheet member.

6 Fixing roller (fixing rotating body)
7 Pressure Rotating Body D Image Forming Device N Nip Part P Paper (Transfer Member)
R Roundness 62 Heating heater (heating means)
71 Pressure belt 72 Pressing member 73 Sheet member 722 Soft pad portion (pressing member)
723 Hard pad part (pressing member)

Claims (4)

A fixing rotator having a heating means and a pressure rotator that presses against the fixing rotator to form a nip portion, and passes through a nip portion through a transferred member having an unfixed toner image formed on one surface. A fixing device that heats and pressurizes the toner image to melt and fix the toner image on the transfer member,
The pressure rotator presses the pressure belt from the inside of the pressure belt and presses against the fixing rotator, and forms a nip portion with the fixing rotator. A pressing member, and a sheet member that is disposed between the pressing member and the pressure belt and reduces a frictional resistance between the pressing member and the pressure belt,
Both end corners of the pressing member in the direction perpendicular to the passing direction of the transferred member have roundness, the roundness is outside the passing region of the transferred member, and at least a part of the roundness is The fixing device is located inside the axial end of the fixing rotator.   The pressing member has a soft pad portion and a hard pad portion that are elongated in a direction perpendicular to the passing direction of the transfer member, and the soft pad portion and the hard pad portion are in this order with respect to the passing direction of the transfer member. 2. The fixing device according to claim 1, wherein at least both corners of the hard pad portion perpendicular to the passing direction of the member to be transferred are rounded.   The fixing device according to claim 1, wherein a radius of curvature of the roundness is 2 mm or more.   An image forming apparatus comprising the fixing device according to claim 1.